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Chromosomal aberrations
- 1. Chromosomal Aberrations Dr. A.S. Wabale Assistant Professor and Research Guide Post Graduate Department of Botany and Research Centre, Padmashri Vikhe Patil College of Arts, Science and Commerce, Pravaranagar- 413 713 dranilwabale78@gmail.com
- 2. CONTENTS Types of structuralchanges in chromosomes A) Deletion: types, cytology and genetic effects B) Duplication: types and cytology, position effect and bar eye phenotype in Drosophila C) Inversion: types and their cytology, D) Translocation: types and translocation complexes E) Variation in chromosome morphology: Isochromosomes, ring chromosomes and Robertsonian translocation April 8, 2021 Dr. A. S. Wabale
- 3. CHROMOSOMAL ABERRATIONS PERICENTRIC PARACENTRIC TRANSLOCATION DELETION TERMINALINTERCALARY SIMPLE TRANSLOCATION AFFECT NUMBER OF GENES AFFECT ARRAGEMENT OF GENES TANDEM REVERSE TANDEM DISPLACED DUPLICATION INVERSION RECIPROCAL TRANSLOCATION MULTIPLE TRANSLOCATION SHIFT TRANSLOCATION April 8, 2021 Dr. A. S. Wabale
- 4. Chromosomal Aberrations: DELETION Deletionor deficiency is a condition in which a small portion of the chromosome is lost resulting in change in the number of genes of that chromosome. Mainly it is of two types 1. Terminal Deletion: A condition in which the terminal part of the chromosome is lost 2. Intercalary or Interstitial Deletion: A condition in which the two break occurs on the chromosome and the part between such breaks is lost, followed by joining of the remaining parts Cytological detection of deletion: It may be detected during meiotic prophase. At the time of synapsis (pairing) a loop is developed on the normal chromosome so as to pair with the chromosome in which deletion had occurred. Deleted portion New Resulted Chromosome Break occurring Normal Chromosome Terminal Deletion Normal Chromosome New Resulted Chromosome Deleted portion Break occurring Intercalary Deletion A B C D E F G H A B C F G H Normal Chromosome Deleted Chromosome Pairing Deleted Chromosome A B C F G H D E Normal Chromosome A B C F G H April 8, 2021 Dr. A. S. Wabale
- 5. Chromosomal Aberrations: DUPLICATION Duplicationis a condition in which a small portion of the chromosome is added resulting in change in the number of genes of that chromosome. Mainly it is of two types 1. Tandem Duplication: A condition in which new segment is just located after the normal one with same gene sequence 2. Reverse Tandem Duplication: A condition in which new segment is just located after the normal one with reverse gene sequence 3. Displaced Duplication: A condition in which new segment is located on the same chromosome but away from the normal segment Normal Chromosome Tandem Duplication Reverse Tandem Duplication Displaced Duplication Cytological detection of duplication: It may be detected during meiotic prophase. At the time of synapsis (pairing) a loop is developed on the duplicated chromosome so as to pair with the normal chromosome A B C D C D E F G DuplicatedChromosome Normal Chromosome Pairing Normal Chromosome A B C D E F G C D DuplicatedChromosome A B C D E F G A B C D E F G April 8, 2021 Dr. A. S. Wabale
- 6. Chromosome Structure Phenotype X-16A X-16A Normal Eye Female X-16A-16A X-16A BarEye Female X-16A-16A X-16A-16A Bar eye female (more restricted, 68 facets) X-16A-16A-16A X-16A Double bar eye female (45 facets) X-16A-16A-16A X-16A-16A-16A Double bar eye female (further reduced) One phenotype that has been analyzed in Drosophila with respect to duplications is bar eye. The eye of the fly is normally an elongated oval shape whereas the bar eye phenotype is much thinner. When the chromosomes of males with bar eye are analyzed, a duplication in region 16A of the chromosome is detected. Another mutant of the eye shape is the double bar eye. These individuals have a second duplication of the same 16A region. The chromosomal environment can have an effect on the expression of a specific gene. i.e. the phenotype of a gene is altered by changes in the position or chromosomal environment of the gene. Such an effect is termed as Position Effect Wild Type (779 facets) HomozygousBar (68 facets) Homozygous Double Bar (25 facets) Position effect and bar eye phenotype in Drosophila April 8, 2021 Dr. A. S. Wabale
- 7. Chromosomal Aberrations: INVERSION Aevent in which two breaks occur in a chromosome, the region between these breaks rotates at 180 degrees and rejoins with the two end fragments refers to Inversion. Unlike deletions and duplications, inversions do not change the overall amount of the genetic material, so inversions are generally viable and show no particular abnormalities at the phenotypic level. Depending upon the involvement of centromere, inversion is of two types: 1. If the centromere is outside the inversion, then the inversion is said to be paracentric 2. If the centromere is within inverted part then the inversion is said to be pericentric PARACENTRIC INVERSION PERICENTRIC INVERSION April 8, 2021 Dr. A. S. Wabale https://www.youtube.com/watch?v=QXU7XojaEOs
- 8. CYTOLOGY OF PERICENTRICAND PARACENTRIC INVERSION April 8, 2021 Dr. A. S. Wabale
- 9. TRANSLOCATION April 8, 2021Dr. A. S. Wabale Translocation is a type of chromosomal abnormality in which a chromosome breaks and a portion of it reattaches to a different chromosome. Chromosomal translocations can be detected by analyzing karyotypes of the affected cells. Translocations may originate spontaneously. They may be induced by mutagens, viz., ionizing radiations and many chemical mutagens, since they induce chromosome breakage. Translocations may be induced by growing plants in calcium-deficient media, as reported by Nilan and Phillips in 1957.
- 10. Translocation may beclassified on the basis of the trans-located segment being present in the same, homologous or non-homologous chromosome and the number of breaks involved in the translocation. 1. Simple Translocation: In this a broken chromosome segment reattaches to another chromosome of the same homologous pair. It is also known as nonreciprocal or intrachromosomal translocation. 2. Shift Translocation: In this a broken chromosome segment reattaches to another chromosome of non-homologous pair. It is also known as nonreciprocal or interchromosomal translocation. 3. Reciprocal Translocation: In this type of translocation breaks occurs on two non-homologous chromosomes and the broken segments are interchanged and reattached Simple or Intrachromosomal Translocation Shift or Interchromosomal Translocation Reciprocal Translocation TYPES OF TRANSLOCATION April 8, 2021 Dr. A. S. Wabale
- 11. MULTIPLE TRANSLOCATION INRHEO DISCOLOR (2n=12) April 8, 2021 Dr. A. S. Wabale A B C D E F G H I J K L A ‘ B’ C ‘ D’ E ‘ F’ G‘ H’ I ‘ J’ K ‘ L’ A B C D E F G H I J K L A ‘ B’ C ‘ D’ E ‘ F’ G‘ H’ I ‘ J’ K ‘ L’ Multiple Translocation New Combinations A L C B E D G F I H K J A ‘ B’ C ‘ D’ E ‘ F’ G‘ H’ I ‘ J’ K ‘ L’ The translocation in which two or more than two pairs of non-homologous chromosomes are involved refers to multiple translocation. This can be explained with Rheo discolor with chromosome number 2n=12. There are several different genetic factor complexes which are combined in the various species. These complexes segregates as wholes in meiosis, each gamete carrying one or other referred as Renner complexes, a phenomenon named after its discoverer Renner, in 1914. The meiocytes of Rheo at diakinesis of meiotic prophase-I show multivalent rings and chains comprising of four, six, eight or all twelve chromosomes. This is because, if the arm of one of the translocated chromosome is involved in a second interchange with third non-homologous chromosome, a ring of chain of 6 would form at metaphase
- 12. A L L’ K’ K J J ’ I’ I H H ‘ G ’ G F F ‘ E ‘ E D D ’ C ’ C B B ‘ A ‘ Pachytene stage MULTIPLE TRANSLOCATION IN RHEO DISCOLOR (2n=12) April 8, 2021 Dr. A. S. Wabale MultivalentRing of 12 Chromosomes Diakinesis stage A L L’ K’ K J J ’ I ’ I H H ‘ G ’ G F F ‘ E ‘ E D D ’ C ’ C B B ‘ A ‘ MultivalentChain of 12 Chromosomes
- 13. An isochromosome isan unbalanced structural abnormality in which the arms of the chromosome are mirror images of each other. The chromosome consists of two copies of either the long (q) arm or the short (p) arm because isochromosome formation is equivalent to a simultaneous duplication and deletion of genetic material. Consequently, there is partial trisomy of the genes present in the isochromosome and partial monosomy of the genes in the lost arm. ISOCHROMOSOME April 8, 2021 Dr. A. S. Wabale
- 14. Robertsonian translocation (ROB)is a chromosomal abnormality where a certain type of a chromosome becomes attached to another. It is the most common form of chromosomal translocation in humans, affecting 1 out of every 1,000 babies born. It does not usually cause health difficulties, but can in some cases result in genetic disorders such as Down syndrome and Patau syndrome. Robertsonian translocations result in a reduction in the number of chromosomes. Robertsonian translocations are named after the American zoologist and cytogeneticist William Rees Brebner Robertson (1881–1941) who first described a Robertsonian translocation in grasshoppers in 1916. They are also called whole-arm translocations or centric-fusion translocations. A Robertsonian translocation effects acrocentric chromosomes. In an acrocentric chromosome, the narrow region where both halves of the chromosome join is near the very end of the chromosome. In a Robertsonian translocation, acrocentric chromosomes fuse together. This fusing joins two “long arms” of DNA into one. As cells multiply, this DNA error is copied over and over, and usually the short arms of the DNA chain are lost. The lost information can result in your DNA appearing one full chromosome short of the normal count of 46. The acrocentric chromosomes in this DNA chain are chromosomes 13, 14, 15, 21, and 22. Common translocation formations include: 1. Chromosome 13 with chromosome 14 (the most common Robertsonian translocation and the most common chromosome rearrangement found in humans) 2. Chromosome 14 with chromosome 21 3. Chromosome 15 with chromosome 21 4. Chromosome 21 with chromosome 22 Since DNA chromosomes are linked together into 23 pairs, having an odd number of chromosomes can sometimes indicate that essential genetic information is missing from your DNA. A Robertsonian translocation can also result in an extra copy of one chromosome being included in your DNA. A DNA chain with missing or extra genetic information is referred to as imbalanced. Multiple miscarriages, difficulty getting pregnant, and pregnancies in which the fetus develops a trisomy or other genetic abnormality could be a sign that has this translocation. https://www.youtube.com/watch?v=vbGw4VanNjk Robertsonian Translocation Normal non-homologous acrocentric chromosomes ROBERTSONIAN TRANSLOCATION April 8, 2021 Dr. A. S. Wabale
- 15. ASSIGNMENT April 8, 2021Dr. A. S. Wabale Que.1) Explain Chromosomal Aberration / Structural changes in chromosomes in brief Que.2) Explain deletion, its types, cytological detection y and genetic effects Que.3) Explain duplication, its types, cytological detection y and genetic effects Que.4) Explain inversion and its types Que.5) Explain pericentric inversion in detail Que.6) Explain paracentric inversion in detail Que.7) Explain translocation and its types Que.8) Explain multiple translocation in Rhoe discolor Que.9) Comment on Robertsonian translocation Que.10) Comment on Isochromosome